The making of a part having a circular peripheral edge has always been difficult when using only those tools one might expect to find in a home workshop. To make parts by hand with circular peripheral edges which are true and repeatable is virtually impossible.
U.S. Pat. No. 3,936,983 teaches a sanding fixture which solves this problem. The fixture is adapted to be mounted on the table of a powered disk sander, grinder or other power tool having a rotary abrasive wheel. In power tools of this type, the abrasive disk rotates in a fixed plane relative to the work supporting table. If the peripheral edge of the circular part is to be non-tapering, the abrasive wheel is oriented in a plane perpendicular to the plane of the work surface of the table.
The prior art fixture comprises a rectangular base plate mountable on the table. The base plate preferably has a longitudinal rib on its underside receivable in a guide slot in the tool table. Alternatively, in the absence of a guide slot the base plate can be securely located on the table with dowels, clamps or the like. A second plate is supported on the first plate and is parallel thereto. The second plate is pivotally affixed to the first plate so as to be shiftable toward and away from the rotary abrasive wheel in a plane perpendicular to the plane of rotation of the rotary abrasive wheel. The extent of pivotal movement of the second plate toward the rotary abrasive wheel is limited by its abutment against a stop mounted on the base plate. The second plate has a plurality of holes located at various distances from its edge which faces the rotary abrasive wheel. A pin may be located in any of these holes to determine the radius of the finished circular part. A roughly circular, oversize workpiece is provided with a central perforation. The second pivoted plate is shifted away from the rotary abrasive wheel by a distance sufficient to enable the workpiece hole to receive the workpiece mounting pin. Thereafter, the second plate is pivoted toward the rotating abrasive wheel until the workpiece engages the abrasive wheel. Pivoting of the second plate continues until it contacts the stop on the base plate, thereby determining the workpiece radius. At this point, the workpiece is rotated on the mounting pin until the entire periphery has been reduced to the desired radius.
Each of the pin mounting holes in the second plate represents a different final radius of the part. When it is desired to make a part with a radius other than the specific radii provided by the holes in the second plate, some sort of shim means must be provided for the stop.
The present invention is directed to an improved fixture of simplified construction which will enable the making of a circular part, the circular peripheral edge of which is true and repeatable. The part may have any radius within the size capability of the fixture, and without the necessity of making special shims or the like.
The fixture of the present invention may be mounted on the work supporting table of any appropriate powered abrasion tool such as a sanding disk, a sanding belt, a grinding disk, and the like. Therefore, while not so limited, for purposes of an exemplary showing the fixture of the present application will be described in its use with the table of a conventional, powered belt sander.